The present invention relates to a method of transmitting a digital video signal through an Asynchronous Transfer Mode (ATM) or a packet switching system, and more particularly to an video signal transmitting method which is suited to reduce degradation of a video on a receiving side when a packet loss (abandonment) is generated on a transmission line.
In packet transmission or a signal transmitting method of transmission in an ATM system, digital information to be transmitted is divided into certain information quantity, and divided digital information is sent in a transmission unit called a packet or a cell (named generically a packet). A packet is composed of a header portion having a fixed length including a packet number, a destination, a parity bit and the like and an information field which is information to be transmitted. That is, digitalized video information is divided by a number of bits which form an information field of a packet, and each division is transmitted as one packet after being added with a header portion.
Conventionally, in a signal transmitting method of packet transmission or transmission by an ATM system of a digital video signal through a packet switching system, synchronization such that a break of a video line (horizontal scanning line), a frame and the like and a break of a packet are in accord with each other has not been taken into consideration, but an analog video signal and a digital video signal formed in a packet have been independent of each other.
With such a composition of a packet, when an error or a loss of data in packet unit is generated on a transmission line, it has been unable to recover such an error or a loss appropriately on a receiving side.
That is, an error on a transmission line occurs at random, and an error rate in bit unit is at a sufficiently low value, 1 bit or less per 10.sup.9 bits, but a packet loss is generated in passing through a packet switching system. For example, packet abandonment occurs due to restriction of traffic volume. In case a packet is abandoned because delay of a packet becomes too much, a burst error in which a plurality of packet becomes too much, a burst error in which a plurality of packets are abandoned is produced in many cases. Even one packet includes several tens of bytes and several packets includes several hundreds of bytes. Accordingly, there has been such a problem that, when a packet loss is produced, picture quality degradation which is detected visually is caused in case a transmission signal covers video information. In video signal transmission of conventional technology, a lost packet number can be detected. In a regeneration portion, however, fixed data are only input in place of a lost packet, and it has been unable to recover to such an extent that picture quality degradation is not caused by error correction or interpolation as video data.